A number of times this afternoon, and a single time a week ago I experienced an issue I hadn't seen before:
I'd be playing just fine, and then my FPS would drop to a single frame every few seconds and not recover. It started when I was in either Shiva HM or my FC plot in the Goblet. Teleporting, changing zones, going to a private instance did not resolve anything.
I checked my game system settings window, and it was still showing my game running at 60 fps (I have it limited down to that), and CPU/Memory/Disk/Network usage on my task manager were all low.
On the last instance I checked my send/received and noticed that sent would stay around 0-30ish instead of the normal range in the mid-hundreds. Received was as normal, in the thousands range.
The other weird symptom is that whatever I was watching at the time (same effect on Netflix and Hulu) would stop. I at first thought that my browser might be the issue, so I closed that but the problem in ffxiv continued. However, when I close FFXIV all of my other network problems went away. This is a first for me; I have a decent connection (34 Mb/s down, 8 up) through TWC and I almost always have one of the aforementioned services running with FFXIV with no issue.
Each time I'd restart FFXIV the problem would go away immediately, and stay gone for a while (maybe as long as an hour, I didn't time it. Late this evening it was gone completely without any further incident.
I play on Gilgamesh (NA) and connect via a wired connection on PC, my character at the time was X'amashi Tia.
PS: I didn't experience any error codes or crashes; I had to disconnect/quit myself---but a number of times when this would happen to me another player would usually be experiencing the bug where they get stuck loading into the instance and the barrier won't go down (this was Shiva HM at the time), if it's relevant.